In DE 197 35 759 A1 a method is described for control of an automatic drive device which has one propeller source, one speed-change transmission with several toothed wheel sets that can be coupled, one fluid-actuatable main clutch and a fluid-actuatable switch means for actuating the individual toothed wheel sets. In addition, an electronic control is provided for the control of the main clutch and of the switch means, the main clutch being retained in a slipping state for attaining a changeover of the switch means free of traction interruptions.
To switch the forward gears, there is provided as coupling element or switch means respectively on a transmission input shaft and on a transmission output shaft, one draw key device actuated by a hydraulic adjusting element for changing over the reduction steps or forward gears. At the same time, two idler toothed wheels, having each two fixed toothed wheels, can be coupled, respectively, upon the transmission input shaft or the transmission output shaft.
Within a central hole in the transmission output shaft, a tappet is movably passed which, as a form-locking coupling element, carries a draw key. The draw key penetrates a radial slot in the input shaft and interacts with longitudinal grooves in the toothed wheels. The length of the radial slot allows an axial displacement of the draw key, via the tappet, from a first position in which the draw key couples with positive fit a first toothed wheel with the transmission input shaft, to a medium idling position in which the draw key produces no connection with positive fit between the transmission input shaft and a toothed wheel and to a third position in which one other toothed wheel of a new ratio step is coupled with positive fit with the input shaft.
In order to make possible a low-wear complete switch of the draw key from one toothed wheel to the other toothed wheel, the cross-section of the opening of a throttle valve of the internal combustion engine is reduced for a brief time interval during the shifting operation independently of an accelerator pedal input so as to reduce the input torque of the internal combustion engine to the range of from milliseconds to tenths of seconds.
However, the above described method for control of an automatic driving device has the disadvantage that during a higher traction shift, the draw key or the switching element has to be disengaged from the toothed wheel, which requires great switching forces. To reduce said switching forces, it has been proposed to reduce the input torque of the internal combustion engine to shifting torque, the drive train of a motor vehicle being completely unloaded by said procedure, which results in an interruption of the traction force.
The problem on which this invention is based is to make a method available for control and regulation of a drive train by means of a higher traction shift being carried out quickly and without traction interruption together with great comfort during shifting.